This invention relates to a shield for emitted radio waves and an image forming apparatus that uses such a shield. More particularly, the invention relates to art that makes the assembly and inspection of such apparatus more efficient.
A shield against emitted radio waves in the conventional image forming apparatus includes a shield box the opening of which is formed to have a flange, and a shield plate secured to the flange using screws that are threadedly engaged with screw holes formed in the flange at prescribed intervals. A board for image processing is secured to the bottom side of the shield box by screws or the like. This arrangement prevents the escape of radio waves emitted from the board for image processing.
An alternative arrangement is shown in FIG. 5, which is an external perspective view of an emitted-radio-wave shield according to the prior art. This shield includes a shield box 201 the opening of which has flanges 201b formed on its four sides 201a, and a shield plate 203 secured to the flanges 201b using screws 210 that are threadedly engaged with screw holes 201c formed in the flanges 201b at prescribed intervals. A board 202 (indicated by the dashed lines) for image processing is secured to the bottom side of the shield box 201 by screws or the like (not shown). Further, the shield plate 203 is secured to the flanges 201b of the shield box via shield members 204 that have been cut to prescribed lengths, thereby reducing the number of screws 210 needed to secure the shield plate 203 to the shield box 201.
With the emitted-radio-wave shield constructed as set forth above, a large number of the screws 210 are necessary to secure the shield plate 203 to the shield box 201. When the board 202 for image processing is accessed, all of the screws 210 must be removed. Such an arrangement has a poor workability.
Further, when shield members 204 are provided, as shown in FIG. 5, it is difficult to provide sufficient flatness for the shield plate 203. As a result, in order to reliably prevent the escape of radio waves from the board 202, securing by way of the screws 210 is required. Though it is possible to reduce the number of screws over the former arrangement, there is still not much improvement in workability.
Accordingly, an object of the present invention is to provide an emitted-radio-wave shield and an image forming apparatus that uses such a shield, the shield being composed of a shield box, which houses a circuit board, and a shield plate, wherein the operation for attaching and removing the shield plate in order to access the board is simplified and leakage of emitted radio waves can be prevented.
According to the present invention, an emitted-radio-wave shield comprises a shield box housing a circuit board; a shield plate removably secured to the shield box; and a shield member, which is disposed at a joint between the shield box and the shield plate and is electrically connected with the shield box, for shielding emitted radio waves from the circuit board in a state in which the shield plate is secured to the shield box; wherein the shield plate is formed to have a plurality of protrusions, which project toward the shield member, at a part thereof that contacts the shield member.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.